BACTERIAL GROUPS IN DECOMPOSING SALMON

Transcription

1 BACTERIAL GROUPS IN DECOMPOSING SALMON ALBERT C. HUNTER From the Microbiological Laboratory, Bureau of Chemistry, United States Department of Agriculture' Received for publication May 24, 192 In a previous paper (liunter, 192) regarding the decomposition of salmon the total counts of bacteria found in the muscular tissue of the back and belly of the fish were given. The occurrence of these bacteria in the viscera and various organs of the salmon in different stages of decomposition was also discussed. The data presented were all obtained from experiments upon salmon handling as conducted in the Puget Sound region. From the mixed cultures and the plates made in the field 3 cultures were isolated and studied with the idea of grouping or typing the organisms significant in the decomposition of the salmon. Special care was taken to select those colonies which predominated on the plates. It was evident that many organisms were obtained -which played no part in the decomposition of the fish and that there were also many duplicates among the original 3 cultures. In order to eliminate the organisms which did not decompose salmon, and to check off the duplicates, use was made of a specially prepared fish broth.2 The 3 cultures were grown in this 1 This work was done under the supervision of Dr. Charles Thom to whom I am indebted for criticism and suggestions. 2 This medium was prepared in the following manner by Mr. B. A. Linden of this laboratory: To 1 grams of finely chopped saltwater trout, or weakfish, from which the skin and bones had been removed, was added 1 cc. of distilled water and 15 grams of peptone. The infusion was made by heating in the Arnold sterilizer or on a water bath at 95 to 1C. for one hour with occasional stirrings. The juice was strained through cheese cloth with a meat press, filtered through cotton and the reaction adjusted to neutral. The infusion was then heated in the Arnold for thirty minutes at 1C. and filtered, using folded filter papers. About 1 cc. was placed in each tube with about 1.5 grams of raw fish. For anaerobic cultures the surface was covered with a layer of liquid petrolatum. The medium was sterilized in the autoclave for fifteen minutes at 15 pounds. 543 TH1 JOURNAL OF BACTERIOLOGY, VOL. V, NO. 6

2 544 ALBERT C. HUNTER medium, aerobically and anaerobically, for one week at 3 C. They were examined daily for the evolution of foul odors and for any digestion of the fish in the bottom of the tube. At the end of one week each culture was tested for indol production with paradimethylamidobenzaldehyde and hydrochloric acid. Only those cultures which produced indol, foul odors, or both, in this medium were saved for further study. In this manner the original number of cultures was reduced to 65 and these organisms were then studied in more detail in order to check the duplicates. The author, however, is aware that, while the discarded organisms had no putrefactive action in pure culture, they may assist in the decomposition of the salmon when associated with the bacteria which have been studied. In spite of this fact the present study has been limited to those cultures producing indol or foul odors when grown in pure culture. On the basis of their morphology and their reactions in litmus milk, gelatin, potato, tryptophane broth and glucose, lactose and sucrose broths these 65 cultures were compared and duplicates eliminated so as to reduce the number to 43. Although some of these 43 cultures were very similar in many respects they all varied sufficiently to be considered different organisms and each of the 43 was studied and identified. Of the 235 cultures rejected as playing no part in the decomposition of the salmon 4 were yeasts, 16 micrococci, 43 streptococci and 172 bacilli of varying morphology. All of the organisms regarded as s'ignificant in the decomposition of the fish are bacilli. Six of the cultures are pigment producers while the remaining 37 produce no pigment. The cultural reactions of these 43 organisms are summarized in tables 1, 2, and 3. For convenience the results are given in three separate tables, table 1 being the reactions of those organisms, exclusive of the pigment producers, which liquefy gelatin, table 2, those which do not produce pigment and do not liquefy gelatin and table 3, those which produce pigment. In studying these bacteria but little attempt has been made to identify any of them, except the pigment producers, as specific organisms. It may be that an extended series of tests in various

3 BACTERIAL GROUPS IN DECOMPOSING SALMON 545 carbohydrate media would identify as species or strains those forms which ferment the sugars but for the purposes of this investigation it has been considered sufficient simply to determine the group to which they belong. The studies of Winslow, Kligler and Rothberg (1919) on the classification of the colontyphoid group and the work of Levine (1918) on the classification of the colon-cloacae group make it possible to identify those bacteria which produce acid, gas, or both, in glucose and lactose. On the other hand the inadequate descriptions in the literature of the non-fermenting bacteria from soil and water made it very difficult to identify unknown organisms of this kind. In table 1 are tabulated the cultural reactions of 2 organisms which liquefy gelatin. Of these 13 have been identified as resembling Bact. cloacae (Jordan, 189) in that they are small, Gram negative, gelatin-liquefying bacilli which produce acid and gas in glucose, lactose and sucrose, give a positive Voges- Proskauer and a negative methyl red reaction. Eight of these 13 cultures differ from the type in the production of indol. Of the remaining 7 cultures described in table 1, 3 are very similar to Bact. formosum as described by Ravenel (1896) while the other 4 resemble nothing described in the literature and evidently belong in a group of unidentified water and soil bacteria. The reactions given in table 2 show that of these 17 cultures 3 resemble Bact. coli, 2 Bact. communior and 3 Bact. aerogenes. The reaction in litmus milk in each case is not always characteristic but the reactions in glucose, lactose and sucrose broths and the results of the methyl red and Voges Proskauer tests would place them in the groups indicated. Culture 7 closely resembles Bact. alcaligenes. The remaining 8 cultures in this table somewhat resemble a number of organisms described by Chester (191) in a group of motile, Gram-negative, non-liquefying bacteria from soil and water which form no spores and do not ferment any of the carbohydrates. The original descriptions of these bacteria, however, are inadequate for identification of the organisms studied. Until further work is done on this group, therefore, they cannot be designated other than as belonging to a large group of unidentified bacteria from the water and soil.

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8 55 ALBERT C. HUNTER Of the 6 cultures producing pigment on gelatin and agar 3 produce an orange pigment, 1 a flesh-colored pigment and 2 a greenish pigment. Cultures 14a, 113b and 18, producing orange pigment, have been found to resemble closely Bact. breve (Frankland, 1894), Bact. caudatum (Wright, 1895) and Bact. aurantiacum (Frankland, 1894) respectively. The organism producing a flesh-colored pigment, 124, iswvery similar to Erythrobacillus carnicolor (Frankland, 1894). The original descriptions of these bacteria are not adequate for positive identification but the reactions of the organisms studied have been found to check with the limited descriptions given in the literature. The two cultures producing green pigment, C and 216, do not closely resemble any bacteria described. These two organisms are undoubtedly identical and might well have been considered as a single culture. All cultures of C and 216 have an aromatic odor. No strict anaerobes and no spore-forming bacteria were isolated from the decomposed salmon. The absence of bacteria of the mesentericus group was surprising in view of the fact that during 1919 an examination of 53 cans of salmon packed in Alaska showed 42 per cent of the cans to contain living bacteria of this group (Hunter and Thom, 1919). No such organisms, however, have been isolated from the salmon caught and packed in the Puget Sound region. In considering the source of the organisms found in the uncooked fish it is evident that neither strict anaerobes nor spore-forming bacteria should be expected. As shown in the previous paper on the subject (Hunter, 192) the digestive tract and viscera of the salmon are sterile when there is no food in the tract and when the fish are examined immediately after they are caught. The presence of bacteria in the gills, mouth and on the skin at all times and the late appearance of these organisms in the digestive tract and in the viscera indicate that the infection after death is from the outside inward rather than from the inside outward as is ordinarily found in the case of warm-blooded animals. We would expect the bacteria in the gills and mouth and on the skin to be those forms, the natural habitat of which is the sea-water in which the salmon live.

9 BACTERIAL GROUPS IN DECOMPOSING SALMON Identification of these 43 cultures has shown that this is actually the case. Most of the bacteria isolated from the decomposed salmon were originally described as water or sewage organisms, although a few were originally isolated from the soil. While these facts do not absolutely preclude the possibility of strict anaerobes and spore-formers being present, actual examination of 3 cultures from a large number of salmon in various stages of decomposition has shown that the flora of decomposed salmon is that of the sea-water from which they were taken. Furthermore, there was apparently no contamination with spore-forming organisms in the boats or in the cannery subsequent to the catching of the fish. The bacteria isolated from fish held for four days in the cannery are the same forms which were isolated from the gills and mouth when the salmon were examined immediately after being caught. The bacteria responsible for the decomposition of the fish are not, in the strict sense, putrefactive and there is no rapid digestion of the flesh of the fish in the cultures. Each culture examined, however, did give some sort of "off" or foul odor in the fish medium and many showed the character of indol production when grown in this medium. It was noted that when grown in a beef infusion broth, with or without a small amount of carbohydrate added, no odors suggestive of decomposition were obtained. This makes it apparent that the flesh of fish is more susceptible to decomposition by ordinary water bacteria than is the flesh of the higher animals. Although the salmon, when not feeding, has no bacteria in its intestines which may play a part in its subsequent decomposition, the accumulation of ordinary water bacteria in the gills and mouth and on the skin provides a flora which brings about a slow decomposition of the body of the fish after death. SUMMARY 551 In a study of the bacteria which decompose raw salmon, 43 cultures were isolated as significant. On identification 21 cultures were found to be members of the colon-cloacae group. One culture resembled Bact. alcaligenes and 3 cultures resembled

10 552 ALBERT C. HUNTER Bact. formosum. Six cultures produced pigment. Twelve cultures not identified to type, evidently belong to a large group of water and soil bacteria which have not been adequately studied. The bacteria isolated from decomposing salmon were found to be those which are described in the literature as water, sewage and soil organisms. REFERENCES CHESTER, F. D. 191 A Manual of Determinative Bacteriology. FLUGGE, C Die Mikro6rganismen, 2, FIIANKLAND, PERCY 1894 Micro6rganisms in water. HUNTER, ALBERT C. 192 Bacterial decomposition of salmon. Jour. Bact., 5, 353. HUNTER, A. C., AND THOM, C An aerobic spore-forming bacillus in canned salmon. J. Ind. and Eng. Chem., 11, 655. JORDAN, E A report of certain species of bacteria observed in sewage. Rpt. Mass. State Board of Health, 189, p LEHMANN, K. B., AND NEUMAN, R Atlas und Grindriss der Bakteriologie. LEVINE, M A statistical classification of the colon-cloacae gvt up. Jour. Bact., 3, 253. RAVENEL, M. P Notes on the Bacteriological Examination of the Soil of Philadelphia. Mem. Nat. Acad. Sci., 8, 3. WINSLOW, C.-E. A., KLIGLER, I. J., AND ROTHBERG, W Studies on the classification of the colon-typhoid group of bacteria with special reference to their fermentative reactions. Jour. Bact., 4, 429. WRIGHT, J. H Report on the results of an examination of the water supply of Philadelphia. Mem. Nat. Acad. Sci., 7, 444.